The present invention relates to a method of forming a silica coating on a substrate. The method comprises applying a silica precursor coating to the substrate and heating it to a temperature above its melting point in an inert environment. The melted coating is then heated in an environment which facilitates conversion to silica for a time sufficient to convert it to silica.
The use of ceramic coatings for their protective and dielectric effect is known in the electronics art. For instance, Haluska et al. in U.S. Pat. No. 4,756,977 disclose silica coatings produced by applying a solution of hydrogen silsesquioxane resin to an electronic device and then ceramifying by heating in air at temperatures of 200.degree.-1000.degree. C. The ceramic coatings produced thereby have many desirable characteristics such as microhardness, moisture resistance, high adhesion, etc.
Similarly, the Accuglass.TM. product literature teaches the use of silicon-oxygen backbone polymers in forming coatings which are useful in microelectronic device processing. This reference describes applying a coating solution comprising the polymer and a solvent followed by consecutive curing of the polymer in air and nitrogen.
Haluska, in U.S. patent application Ser. No. 07/683,908, also describes applying a silicon-containing coating to a substrate. The method taught therein comprises coating the substrate with a solution comprising a solvent and one or more preceramic materials. The preceramic material is then ceramified by heating at temperatures in the range of about 500.degree. to about 1000.degree. C. under an inert gas atmosphere.
The present inventors have now discovered that sequential heating first in an inert environment and then in a reactive environment which facilitates conversion to silica produces coatings having improved planarity and reduced cracks in comparison to conventionally formed silica coatings.